The present invention concerns a glide-shoe arrangement for a variable-crown roll, the roll comprising a non-revolving massive central axle on which a cylindrical roll mantle is journalled to rotate, with piston-glide-shoe combinations being fitted between the axle and inner face of the roll mantle and being loaded by means of hydraulic pressure. The glide shoes can be loaded against the inner face of the roll mantle by means of hydraulic fluid pressure through intermediate pistons, for the purpose of controlling the distribution of nip pressure in a nip situated to face the loading shoes. The piston-glide shoe combinations include cylindrical bores or equivalent formed in the axle, into which substantially cylindrical or equivalent pistons are fitted.
Several different types of variable-crown or adjustable-crown rolls for paper machines are known in the prior art. As a rule, these rolls comprise a massive, stationary roll axle and a roll mantle arranged to rotate about the axle. A series of glide shoes and/or chambers of pressure fluid are fitted between the axle and the mantle to act upon the inner face of the mantle. As a rule, the nips formed by such rolls, such as press nips or calendering nips, are loaded by means of loading forces applied to the axle journals of the variable-crown roll and of its counter-roll.
The present invention relates to such variable-crown or adjustable-crown rolls which include a series of glide shoes having glide faces acting upon the inner face of the roll mantle, with the glide faces being at least partially hydrostatically lubricated by means of pressure fluid passed onto the glide faces.
With respect to the prior art related to the present invention, reference is made by way of example to U.S. Pat. No. 4,241,482, Finnish Pat. Nos. 56,252 and 69,684, and to Finnish Patent Application No. 792,712.
A great number of different functions are required from the supporting and loading members used in variable-crown rolls and acting upon the inner face of the roll mantle and loaded by means of pressurized fluid. Integration of all of these functions in one and the same member has not been quite successful by means of the arrangements known in the prior art. A listing of certain of the properties required in the supporting and loading members is as follows:
the hydrostatic lubrication spaces or chambers of the support shoes as well as of the loading-shoe/cylinder must be sufficiently well-sealed even with varying load forces, and even when changes in angle occur between the mantle and the inner part of the roll;
the loading pistons of the support shoes must receive lateral forces which are caused by friction;
the loading equipment for the support shoes must be capable of functioning as an articulated joint, because the relative positions of the mantle to be supported and the central axle with respect to one another vary to a considerable extent with varying load forces;
the pistons of the support shoes must provide sufficient radial force with a variation range that must be sufficiently large in view of supporting and loading the mantle;
it must be possible to control the thickness of the oil film that lubricates the glide face of the support shoes; and
the loading pistons of the support shoes and the bores provided in connection with the central axle must permit even considerable radial movement of the pistons.
In the loading and supporting members known in the prior art, the functions listed above are not all carried into effect satisfactorily, at least not all of these above-listed functions together.